The invention relates generally to nuclear reactors, and more particularly to apparatus for servicing the core of a nuclear reactor.
In nuclear reactors, it is generally necessary to provide neutron absorber control elements as well as various types of instrumentation for servicing the nuclear core, particularly during operation. Such servicing elements typically enter the reactor through penetrations in a head portion of the reactor. In some instances separate penetrations are provided for the neutron absorbers and others for the instrumentation and in other instances a neutron absorber and instrumentation may be combined in a single package, there being a multiplicity of such arrangements for a reactor.
Further, in certain types of reactors, particularly liquid metal fast breeder reactors, it may be desirable to refuel the reactor without removing the head. This aids in preventing the mixing or contact of liquid metal coolants such as sodium with air and further avoids the release of fission gases. To accomplish the refueling, rotating plugs or shields which serve to close off and seal the reactor vessel during normal reactor operation have been used previously. One example of such an arrangement is seen in U.S. Pat. No. 3,354,040 to A. G. Frame et al. While that patent shows a single large rotating head with a mechanism which transfers fuel between the core and a magazine housed within the environment of the core, other such reactors have incorporated one or more smaller rotating plugs within the larger plug and provide fuel transferring apparatus for removing the fuel entirely from within the reactor vessel. In any event, it becomes desirable to reduce the number of penetrations through the head and/or to reduce the size of each penetration. Such reduction in numbers of penetration and size of penetration serves both to enhance the strength of the head and to allow the greater flexibility in the placing of the fuel handling apparatus and any smaller rotating plugs within the area of the large rotating head portion.
While the above mentioned Frame patent does combine several instrument packages with a neutron absorber actuator for each core servicing assembly which penetrates the rotating head, the lateral dimension of the head penetration required to receive such a servicing assembly is relatively large, creating the drawbacks mentioned above.